A type of variable valve mechanism is known that performs linking and de-linking between a low-speed rocker arm that depresses a valve and a high-speed rocker arm that does not directly depress a valve.
(a) For example, in a variable valve mechanism disclosed in Japanese Patent Application Publication No. JP-A-2005-23803, a nose of a high-speed cam is set higher than that of a low-speed cam, and during low-speed operation, the two rocker arms are de-linked, with only the low-speed rocker arm being rocked by the low-speed cam and opening and closing the valve. Further, during high-speed operation, the two rocker arms are linked into a single unit that is rocked through a larger range by the high-speed cam than during low-speed operation, thus changing the amount of valve lift.
However, because this variable valve mechanism rocks both of the rocker arms as a single unit during high-speed operation, the inertial mass becomes greater than during low-speed operation. Because the inertial mass becomes greater, the need arises to increase the valve spring load in order to reach the target revolution speed of the internal combustion engine. This results in increased friction when the valve is being driven, which diminishes performance and worsens fuel economy. It also becomes necessary for the rocker arms and cam followers to have sufficient strength to bear high loads, which increases the cost.
(b) In a variable valve mechanism disclosed in Japanese Patent Application Publication No. JP-A-2002-21518, a nose of a high-speed cam is set higher than that of a low-speed cam, in the same manner as the variable valve mechanism described above, but during low-speed operation, the two rocker arms are linked into a single unit and open and close the valve by being rocked by the low-speed cam. Further, the two rocker arms are de-linked during high-speed operation, such that only the high-speed rocker arm is rocked through a larger range by the high-speed cam than during low-speed operation, thus changing the amount of valve lift.
A switching mechanism that is provided in the variable valve mechanism links the two rocker arms into a single unit and rocks them during low-speed operation, but the configuration is such that the high-speed cam does not have any effect on the rocking. Specifically, the high-speed rocker arm is provided with a follower that slides against the high-speed cam and with a follower hole. During low-speed operation, the follower slides idly within the follower hole such that the high-speed cam does not have any effect on the high-speed rocker arm. During high-speed operation, the switching mechanism uses a switching pin to cause the follower not to slide idly, such that the high-speed cam causes the high-speed rocker arm to rock.
However, the variable valve mechanism must be provided not only with the switching mechanism for the rocker arms, but also with a mechanism that controls the movement of the follower, which makes the structure more complex.